The invention relates generally to hypersonic ignition systems and more particularly to improving packaging efficiency and reducing weight in a hypersonic vehicle while meeting logistics constraints for an operational system. A paramount logistical consideration is that the integrated weapon and ignition system must be tactically compliant and meet Insensitive Munition (IM) requirements.
Hypersonic vehicles are generally defined as vehicles that operate at speeds higher than Mach 5. There are a number of challenges in operating at this speed. Achieving high supersonic and hypersonic speeds is commonly done using a ramjet or scramjet engine. However, since these engines cannot provide thrust at zero airspeed, an assisted take-off is used, requiring that ignition of the ramjet or scramjet engine take place when the vehicle is operating at supersonic speeds or above. Consistent, reliable ignition of fuel at these speeds has been problematic.
For hypersonic vehicles, cold-start refers to the situation immediately following boost to take-over Mach number conditions (typically around Mach 3 for Ramjets and Mach 5 for Scramjets) and the establishment of airflow through the engine. Prior to ignition, the liquid hydrocarbon fuel is still cold and is not sufficiently reactive to self-sustain combustion. The ignition system must therefore supply both initial ignition energy as well as sustaining energy until the fuel absorbs enough heat for the combustion process to be self-sustaining. For ground tests and early flight testing, this problem has been overcome by the use of an igniter fuel, such as pyrophoric gaseous silane (SiH4), TEA/TEB (a mixture of triethylaluminum and triethylborane), or gaseous Ethylene. These serve to overcome the cold start problem, however, none of the options is logistically suitable for tactical weapon applications. Gaseous Ethylene requires a spark ignition system for cold start; it is highly flammable and is not expected to meet IM requirements. TEA/TEB and Gaseous Silane are difficult to store long term, since they are pyrophoric (undergoes spontaneous ignition in air), highly toxic, and can spontaneously ignite at temperature less than 130° F. Both ignition sources present storage and handling problems and TEA/TEB must be stored in Nitrogen or Argon. Tactical weapons are typically designed to be stored at temperatures from −40° F. to +160° F.
In addition to ignition systems, hypersonic vehicles have other systems that need a supply of gas, including pressurization systems and barbotage systems. Pressurization systems in a hypersonic vehicle are used, for example, to improve the functioning of fuel pumps by providing a constant pressure inlet conditions to the pump.
A barbotage, or effervescent atomization system involves introducing a small amount of high-velocity gas into a very low velocity liquid, leading to turbulent two-phase flow that can improve penetration and vaporization of the fuel jet spray. The difference in the densities of liquid and the gas and the shear interaction between the two phases help break the liquid into smaller droplets and reduce the flow dimensions for the liquid, atomizing the liquid fuel so that it is injected as very fine droplets. This complex phenomenon of supersonic combustion involves turbulent mixing, shock interaction and heat release in supersonic flow.
In the prior art, separate sources have been used to supply these systems, adding weight arising from duplication of equipment in addition to complex wiring and piping.
Thus, a need exists for an ignition and pressurization system for a hypersonic vehicle that has reduced weight and complexity. There is also a need for an ignition and pressurization system that is, volumetrically and resource efficient.